The present invention is generally related to control techniques used in power systems and, more particularly, is related to a power system and control techniques that may be used in combination with reformer-based fuel cells so as to utilize the advantages of such fuel cells while overcoming undesirable transient response characteristics the reformer-based fuel cell may have.
It is known that standard fuel cell stacks that operate directly from a predetermined chemical fuel, e.g., hydrogen fuel, in combination with a predetermined oxidant, e.g., oxygen, provide power response that is sufficient for propelling vehicles, including passenger cars, trucks, and transit buses. It is believed several prototype fuel cell transit buses using hydrogen or other fuels may be in pilot operation in the United States. Various factors, such as safety, governmental regulations, infrastructure and packaging constraints, etc., are forcing other alternatives to direct hydrogen-powered fuel cells for transportation applications. Reformer technology is currently being developed and used to produce hydrogen fuel from alternate fuels, including methanol, gasoline, etc.
When hydrogen produced by a reformer is used to power the fuel cell stacks, unfortunately, the transient power response of the overall system that powers one or more traction motors in the vehicle is typically several seconds or possibly ten seconds or more. Thus, presently available reformer-based fuel cell systems will typically have a severe transient response performance degradation, making such systems unacceptable for transportation applications, power distribution devices, hoisting applications, etc. Further, as in a standard gasoline or diesel engine internal combustion engine (ICE), the standard fuel cell stack and reformer system provides a unidirectional source of power during the process of consuming fuel, and cannot operate in the reverse direction, i.e. accept power and regenerate the chemical fuel during periods of vehicle deceleration. Thus, any energy regenerated by the traction motors during such periods of deceleration would generally be dissipated and wasted.
Thus it is desirable to provide techniques that would allow for a highly efficient power control system that using a suitable energy storage device would solve the undesirable slow transient power response of standard fuel cells operating with a reformer. It would be further desirable to provide techniques that would allow for recovering or capturing in the energy storage device energy that may be generated during periods of deceleration, e.g., when the traction motors in the vehicle act as generators of electricity, as opposed to generators of mechanical power.